Project Summary It is now recognized that the extracellular matrix (ECM) provides a bioactive environment in lungs (and other organs) that orchestrates cellular function for tissue morphogenesis, homeostasis, wound healing, and disease. Our published work and preliminary data using airway biopsies from subjects with and without asthma, mouse models, and in vitro cell cultures show that the ECM molecule, versican (gene = Vcan), accumulates in the lower airways and is strongly correlated with inflammation and airway hyperresponsiveness (AHR). We have found that versican is synthesized in response to allergens from at least two sources: fibroblasts and macrophages and that versican has a dramatic effect on leukocyte phenotype, adhesion and migration. To better understand the mechanisms whereby versican modulates the immune response to allergens, we propose to use two novel strains of mice with conditional deficiency in versican. These include Vcan-/- mice, which have a global deletion of versican when treated with tamoxifen; and LysM/Vcan-/- mice which lack versican in myeloid cells. The Vcan-/- and LysM/Vcan-/- mice have strikingly different pulmonary inflammatory responses, as summarized by three major findings: 1) stromal cells (e.g., fibroblasts) synthesize a form of versican that promotes the development of a pro-inflammatory ECM; 2) macrophage-derived versican restrains airway inflammation, which our preliminary data suggest is conferred by the selective expression of the V3 isoform of versican by macrophages; and 3) signaling pathways regulating versican expression in fibroblasts and macrophages differ, with the WNT/?-catenin/T-cell factor (TCF) pathway regulating Vcan expression in fibroblasts and, as we recently defined, the TLR/Trif/Type I interferon (IFN) pathway in macrophages. Our preliminary and published observations underscore the importance of understanding the immunomodulatory properties of versican and are the basis for our central hypothesis that allergens such as HDM increase the production of fibroblast-derived versican forming a pro-inflammatory ECM that promotes airway inflammation and AHR leading to chronic asthmatic conditions. Conversely, macrophage- derived versican forms an anti-inflammatory ECM. This hypothesis will be tested through completion of our two aims: Aim 1. Identify the role of fibroblast- vs. macrophage-derived versican in airway inflammation and AHR caused by HDM allergen and the mechanisms regulating Vcan expression in these cells. Aim 2. Define the mechanisms by which the structural components of versican promote or restrain airway inflammation through the formation of a pro- or anti-inflammatory ECM. Understanding the contextual settings in which versican provides fine control of airway inflammation and AHR is critical for the development of therapeutic strategies for improving outcomes in patients with asthma.